Method of cleaning returnable bottles

ABSTRACT

A method for cleaning returnable bottles and similar containers used in the food industry. The method uses an enzymatic solution during the cleaning process. The cleaning results are at least as good as conventional methods, without requiring an increase in the duration of cleaning. The method substantially reduces bottle corrosion and waste water pollution compared to conventional methods.

BACKGROUND OF THE INVENTION

This invention relates generally to institutional cleaning and moreparticularly to an automatic “mild” process for cleaning returnablebottles and other reusable containers designed to hold foods.

Many foods, more particularly dairy products and beverages, are beingincreasingly sold in reusable packs which, after emptying, are returnedby the customer and may be reused as a pack for the same foods. Examplesof foods thus packaged are milk, cocoa, cream, yoghurt, mixed milkdrinks, mineral waters, fruit juices, beer, lemonade, soft drinks andother mixed beverages. The returnable containers may consist of variousmaterials, more particularly glass or plastics, such as polycarbonate(PC), polyvinyl chloride (PVC), polyesters (for example polyethyleneterephthalate, PET, or polyethylene naphthenate, PEN) and polyethylene(PE). The containers may be adapted in shape to a variety ofapplications. Thus, bottles are preferably used for liquids while cupsor cans are preferably used for foods with a pasty, gel-like or solidconsistency. In the interests of simplicity, the present specificationrefers solely to bottles or the cleaning of bottles in the followingalthough other containers to be cleaned in this way and their cleaningare of course also meant to be included.

It is obvious that the used bottles returned by the consumer have to becleaned in a hygienically satisfactory manner before they are re-used.In the institutional sector, this is normally done using fully automaticcleaning machines in which the bottles are conveyed through severalcleaning zones. These cleaning machines differ in construction accordingto the nature of the containers and the foods used. In general, themachines comprise at least one pre-rinse zone. In at least one otherfollowing zone, the containers are treated with a cleaning solution atelevated temperature. Finally, there is at least one other zone in whichthe bottles are rinsed with water. The prerinse zone is also oftenreferred to as the presoak zone and the zone in which the containers aretreated with the cleaning solution as the “liquor” zone. Severalseparate zones may be present both for the prerinse phase, the cleaningphase and the final rinse phase. Depending on the particularapplication, other zones, for example a preliminary bottle emptyingzone, may be provided. The contacting of the bottles with the cleaningliquids can take place differently in each zone, generally by sprayingor immersion. As they pass through the machine, the bottles are normallyfirst heated slowly in the precleaning zone, are then treated at a muchhigher temperature in the liquor zone and, thereafter, are cooled againin the following rinse zones. By virtue of this division into differentbaths and zones, detergents, water and heat are economically andeffectively used.

After loosely adhering food residues and soils have been removed in theprerinse zone, the bottles are actually cleaned in the liquor zone. Thiszone comprises at least one station where the bottles are cleaned with acleaning solution at high temperatures of normally about 60 to 90° C.,depending on the bottle material. Particularly good cleaning effects areobtained where one to three liquor baths are combined with a followingliquor spray zone. Conventional cleaning processes use as liquor acleaning solution which contains ca. 1 to 3% of sodium hydroxide andadditions of sequestering agents, surfactants and other detersivecomponents. Hitherto, the belief was that satisfactory cleaning of thebottles in a short time could only be achieved with liquors as highlyalkaline as this notwithstanding the disadvantages of using suchcleaning solutions. Thus, the use of strongly alkaline liquors placed aheavy burden on wastewater treatment plants which was further increasedby the presence in these strongly alkaline liquors of certainnon-readily biodegradable auxiliary chemicals. In addition, the surfacesof glass bottles and various plastic bottles were attacked under theextreme conditions so that the bottles soon assumed an unattractiveappearance and, in many cases, even had to be removed from the circuitat an early stage. The saponification of fat-containing residues oftenresulted in problems with foam. Defoamers had to be added as acountermeasure. Their critical wash-out behavior gave them the potentialto contaminate the food to be packaged. Finally, the use of stronglyalkaline cleaning liquors exposed the machine operator to a significantrisk, of “burning”.

BRIEF SUMMARY OF THE INVENTION

Starting out from these observations, the problem addressed by thepresent invention was to provide an improved process for cleaningbottles which would avoid the disadvantages of conventional processeswithout any deterioration in the cleaning result.

It has surprisingly been found that this problem can be solved by theuse of an enzyme-containing cleaning solution in the cleaning zone.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, the present invention relates to a process for cleaningreturnable bottles and similar containers designed to hold foods, inwhich the used bottles are conveyed through several zones in a bottlewashing machine of which at least one zone is intended for prerinsing,at least one following zone for treatment with a cleaning solution atelevated temperature and at least one other zone for rinsing with water,at least one enzyme being added to the cleaning solution to boost itscleaning performance. Enzymes from the group of proteases, amylases,cellulases, lipases, oxidoreductases and mixtures of these enzymes arepreferably used. The use of proteases, especially highly alkalineproteases, on their own or together with other enzymes is particularlypreferred.

The present invention also relates to the use of a correspondingsolution in the process described above.

Surprisingly, it is possible by the new process to achieve an at leastequivalent result in the same short times as with conventional highlyalkaline cleaning liquors, but at distinctly lower temperatures anddistinctly lower pH values. In many cases, a far better cleaning resultis achieved than with conventional highly alkaline cleaning liquorsdespite a lower concentration of active substance in the cleaningliquor. The possibility of using lower concentrations of detersivechemicals and biodegradable active substances makes the new processparticularly environmentally friendly. The corrosion of the bottlesurfaces is negligible and, in addition, energy is saved through the lowworking temperatures.

According to the invention, suitable enzymes are any enzymes which havea degrading effect on the food remains and soils to be removed. Theabove-mentioned enzymes from the group of proteases, arnylases,cellulases, glycosidases, lipases and oxidoreductases are particularlypreferred. Through the choice of various enzymes, the cleaning processcan be specifically adapted to the particular food residues to beremoved. Thus, proteases are preferably used for removingprotein-containing soils while amylases are preferably used forstarch-containing soils and lipases for removing fatty soils. Thecombination of several enzymes for different substrates is recommendedin cases where mixed soils are present. Accordingly, proteases aremainly used for the preferred application of the process according tothe invention for cleaning bottles used for dairy products, moreespecially milk bottles. The use of so-called highly alkaline proteaseswhich have an isoelectric point above pH 10 and optimal activity at a pHof about 9 to about 12 is particularly preferred. The most importantrepresentatives of this group of enzymes include certain representativesof the serine proteases known as subtilisins which are obtained frombacteria and which, as a sub-group, have acquired the common name ofI-S2 in the scientific literature. This group includes, for example, theenzymes known as subtilisin 147, subtilisin 309 and subtilisin PB92 (seealso R. J. Siezen et al, Protein Engineering, Vol. 4, No. 7, 719-737(1991)). Highly alkaline proteases are also commercially available asenzyme preparations, for example under the names of SAVINASE®,ESPERASE®, DURAZYM®, MAXACAL®, PLURAFECT®, OPTICLEAN® and BLAP®. Besidesthe actual active enzyme, these preparations generally containrelatively large amounts of stabilizers and carriers.

The enzyme content is normally not expressed in percent by weight, butinstead in standardized manner as activity units, i.e. for the proteasesthe available protein-splitting activity in the particular enzymepreparation or in the enzyme-containing solution. In the following, theunit KNPU (Kilo Novo Protease Units) introduced by the Novo Company isused for proteases; other units may require a corresponding conversion.In the case of proteases, the enzyme solution used in accordance withthe invention should preferably contain about 0.16 KNPU to about 160KNPU and more particularly about 0.8 KNPU to about 80 KNPU per liter.The range from about 1.6 KNPU to about 16 KNPU per liter of cleaningsolution is particularly preferred. The content of the other enzymes issimilarly measured in the following units:

unit for amylase: MWU (Modified Wohlgemut Unit)

unit for lipase: KLU (Kilo Lipase Unit). 0.2 to 100 units of theseenzymes are preferably used per liter of cleaning solution. Basically,however, the necessary quantity of enzyme is always determined by theparticular cleaning problem to be solved so that quantities larger orsmaller than those mentioned above may readily be used in individualcases.

The cleaning solution used in accordance with the invention ispreferably prepared from the highly concentrated liquid or powder-formenzyme preparations offered by various manufacturers. The blendingagents, auxiliaries and solvents added to these enzyme preparations thenalso become part of the cleaning solution. The preparations of highlyalkaline proteases commercially available under the names of SAVINASE®,MAXACAL® and BLAP® are particularly preferred for the process accordingto the invention.

The final enzyme-containing cleaning solutions intended to act on thebottles generally have a weakly alkaline pH which is preferably betweenabout 8 and about 12 and more particularly between about 8.5 and about9.5 (as measured at 20° C.). A pH well below the value at the maximumactivity of the enzyme is selected above all when the activity of theenzyme in the cleaning solution is to be maintained for prolongedperiods. The pH can be adjusted in known manner, for example by usingbuffering agents or even by a device for automatically dispensing thenecessary quantity of alkali.

In the process according to the invention, the cleaning solution isintended to act on the bottles at elevated temperature, temperatureswell below those used in the hitherto known cleaning of bottles withhighly alkaline solutions being sufficient. The contact temperatures arepreferably between about 30 and about 70° C. and more particularlybetween about 40 and about 55° C. Despite these low contacttemperatures, the contact times required to obtain a satisfactorycleaning result are no longer than in conventional cleaning processes.

Besides the constituents already mentioned, the enzyme-containingcleaning solutions used in accordance with the invention may containother active substances and auxiliaries. Surfactants for boosting thecleaning effect are mentioned above all in this regard. Basically,surfactants from any known classes may be used. However, nonionic,cationic and amphoteric surfactants are preferred, the nonionicsurfactants having the greatest importance. Examples of otherauxiliaries and additives are enzyme stabilizers, such as solublecalcium salts and borates, compounds with a threshold effect, complexingagents, builders, thickeners, antioxidants, foam inhibitors andpreservatives. In selecting these auxiliaries/additives, it is importantto ensure that they do not interact undesirably with one another or withthe enzymes.

Suitable nonionic surfactants are in particular the addition products oflong-chain alcohols, alkyl phenols, amides and carboxylic acids withethylene oxide (EO) and optionally together with propylene oxide (PO).These include, for example, the addition products of long-chain primaryand secondary alcohols containing 12 to 18 carbon atoms in the chain,more particularly fatty alcohols and oxo alcohols of this chain length,with 1 to 20 moles EO and the addition products of fatty acidscontaining 12 to 18 carbon atoms in tie chain with preferably 2 to 8moles ethylene oxide. The mixed addition products of ethylene andpropylene oxide and C₁₂₋₁₈ fatty alcohols, more especially thosecontaining about 2 moles EO and about 4 moles PO in the molecule, areparticularly preferred. Depending on the embodiment, the open terminalfunctional alcohol group may also be end-capped by an alkyl group. Thealkyl group is preferably a methyl or butyl group. Examples of suitablenonionic surfactants are the fatty alcohol alkoxylates marketed byHenkel KGaA under the names of DEHYPON® LS24, DEHYPON® LS54, EUMULGIN®05, DEHYDOL® LT8, DEHYDOL® LT6, DEHYDOL® LS6 and DEHYDOL® LT104. Othersuitable nonionic surfactants are the esters of C₆₋₁₂ fatty acids andpolyols, more particularly carbohydrates, for example glucose. Wherenonionic surfactants are present in the cleaning solutions used inaccordance with the invention, their content therein is preferably about0.001 to about 0.08% by weight and more particularly about 0.01 to about0.05% by weight, based on the ready-to-use cleaning solution.

Suitable cationic surfactants are, in particular, aliphatic andheterocyclic quaternary ammonium compounds and quaternary phosphoniumcompounds which contain at least one long-chain C₈₋₁₈ alkyl group at thequaternary center. Examples of such cationic surfactants are cocoalkylbenzyl dimethyl ammonium chloride, dioctyl dimethyl ammonium chlorideand tributyl tetradecyl phosphonium chloride.

Suitable amphoteric surfactants are, in particular, C₈₋₁₈ fatty aidamide derivatives of betaine structure, more particularly derivatives ofglycine, for example cocoalkyl dimethyl ammonium betaine. Cationic andamphoteric surfactants are used in the cleaning solution in quantitiesof preferably not more than 0.08% and more particularly between 0.001and 0.02% by weight.

Suitable threshold-effect compounds are polyphosphates, phosphonic acidsand polycarboxylates. Suitable polyphosphates are, in particular,orthophosphate, pyrophosphate, tripolyphosphate, tetrapolyphosphate,hexametaphosphate. Suitable phosphonic acids are, above all,nitrilotrimethylene phosphonic acid, hydroxyethane diphosphonic acid,phosphonobutane tricarboxylic acid and other derivatives of phosphonicacid. Suitable polycarboxylates preferably come from the class ofpolyacrylates, polysuccinates, polyaspartates or other salts ofpolyorganic acids. Suitable builders are the already mentionedpolyphosphates, phosphatonates, gluconates, citrates, EDTA, NTA andother complexing agents suitable as builders. Threshold-effect compoundsare used in quantities of preferably about 0.002 to about 0.05% byweight and more particularly about 0.004 to about 0.02% by weight, basedon the final cleaning solution.

To prepare the cleaning solution used in accordance with the invention,the individual constituents may in principle be separately added to anddissolved in the water. However, it is more appropriate to start withconcentrates prepared in advance which contain several or preferably allof the constituents in the correct mixing ratio so that only a few“dosing” steps or only one are/is necessary. Liquid concentrates areparticularly easy to dose although concentrated formulations in the formof powders, tablets or pastes are also suitable. Additional constituentsof liquid concentrates include solubilizers, such as cumene sulfonate,xylene sulfonate and octyl sulfonate although other typical solubilizersmay of course also be used. The solubilizer content is selected asrequired and is preferably about 1 to about 10% by weight and moreparticularly about 2 to about 5% by weight, based on the concentrate asa whole. Liquid concentrates may additionally contain relatively largequantities of organic solvents, especially polyols, for examplepropylene glycol or glycerol. General formulations for a liquidconcentrate and a solid concentrate are given below:

Liquid Cleaning Concentrate:

enzyme, especially protease 1 to 10, preferably 3 to 6% by weightpropylene glycol 5 to 80, preferably 20 to 40% by weight glycerol 5 to20, preferably 5 to 8% by weight nonionic surfactant 2 to 40, preferably5 to 25% by weight enzyme stabilizer 1 to 10, preferably 2 to 5% byweight quaternary ammonium compound, for example dioctyl dimethylammonium chloride 1 to 40, preferably 2 to 5% by weight balance to 100%by weight water

Solid Cleaning Concentrate:

enzyme, especially protease 1 to 10, preferably 3 to 6% by weight sodiumand/or potassium carbonate 5 to 50, preferably 10 to 30% by weightsodium and/or potassium bicarbonate 5 to 50, preferably 10 to 30% byweight nonionic surfactant 2 to 40, preferably 5 to 25% by weightquaternary ammonium compound, for example dioctyl dimethyl ammoniumchloride 1 to 40, preferably 2 to 10% by weight sodium and/or potassiumtriphosphate 1 to 30, preferably 3 to 10% by weight phosphonate 0.5 to5, preferably 1 to 3% by weight

The concentrates are normally added to the water in quantities of about0.05 to about 0.5% by weight and preferably in quantities of 0.1 to 0.2%by weight to obtain a cleaning solution ready to use for the processaccording to the invention.

EXAMPLES

The cleaning test was carried out in a one-ended bottle washing machineof the type often encountered in practice and marketed by suchmanufacturers as Krones, KHS or Simonazzi. The treatment sequence in themachine comprised two presoak stages, a liquor soaking zone, two liquorspray zones, an “after-liquor” zone, two warm water baths with spraynozzles for rinsing out the cleaning solution and a cold water zone withfresh water spray nozzles.

The object of the cleaning test was to clean heavily soiled glass milkbottles returned by consumers to the milk bottling plant as normalreturns within the liquor treatment time (liquor soak, liquor spray andafter-liquor) of ca. 8 minutes.

First, the test was carried out with 50,000 dirty bottles in aconventional cleaning liquor. This liquor contained an aqueous solutionof ca. 2% NaOH, 0.02% sodium gluconate, 0.02% sodium citrate, 0.04%DEHYPON® LT 104, 0.02% NTA. The total contact title including immersionand spraying was ca. 8 minutes while the contact temperature was about85° C. Visual inspection showed 258 of the 50,000 bottles to be notentirely clean.

After this test, the entire cleaning solution was drained off and afresh solution prepared. The new cleaning solution contained an aqueoussolution of ca. 0.005% ESPERASE®, 0.036% butyl glycol, 0.020% DEHYPON®LT104. The total contact time was again ca. 8 minutes while the contacttemperature was about 50° C. Of 50,000 dirty bottles, only 26 werevisually identified as having residues after the cleaning test.

What is claimed is:
 1. A process for cleaning returnable bottles orcontainers designed to hold foods, the process comprising the steps of:a. conveying the bottles or containers through several zones in a bottlewashing machine, the several zones comprising a zone for pre-rinsing, atreatment zone following the pre-rinsing zone for treatment with anaqueous cleaning solution at a pH of about 8 to about 12 and atemperature of about 30° to about 70° C. and a zone following thetreatment zone for rinsing with water; and b. washing the bottles orcontainers in the treatment zone with said aqueous cleaning solutioncomprising: i. at least one enzyme chosen from the group consisting ofproteases, amylases, cellulases, lipases, and oxidoreductases: ii. atleast one polyol; and iii. at least one non-ionic surfactant comprisingan addition product of a 12-18 carbon alcohol and ethylene oxide orpropylene oxide wherein the addition product is end-capped by an alkylgroup.
 2. A process as in claim 1, wherein the bottles or containers aretreated with the aqueous cleaning solution at temperatures of 40° C. to55° C.
 3. A process as in claim 1, wherein the aqueous cleaning solutioncomprises at least one protease.
 4. A process as in claim 1, wherein theaqueous cleaning solution has a pH of about 8.5 to about 9.5.
 5. Aprocess as in claim 1, wherein the aqueous cleaning solution comprisesat least one additive selected from the group consisting of surfactants,buffering agents, enzyme stabilizers, polyphosphates, phosphonic acids,polycarboxylates, complexing, agents, builders, thickeners,antioxidants, foam inhibitors and preservatives.
 6. A process as inclaim 1, wherein the aqueous cleaning solution is prepared from aconcentrate by diluting the concentrate with water.
 7. A process as inclaim 3, wherein the protease is an alkaline protease having optimalactivity at a pH of about 9 to about
 12. 8. A process as in claim 3,wherein the aqueous cleaning cleaning solution comprises 0.16 to 160KNPU of protease per liter.
 9. A process as in claim 7, wherein theprotease is a subtilisn.
 10. A process as in claim 8, wherein theaqueous cleaning solution comprises 0.8 to 80 KNPU of protease perliter.
 11. A process as in claim 8, wherein the aqueous cleaningsolution comprises 1.6 to 16 KNPU per liter.